Long-sleeved base layer tops in breathable synthetic fabrics or merino wool are multi-talents that'll take you from autumn to spring. Worn underneath a cycling jersey, they're the foundation of the breathable onion principle. They absorb moisture during exercise, transferring it over a large surface area to the next layer up – and ensuring a pleasantly dry climate on your skin. Many of these long-sleeved tops also look good worn alone and offer an airy alternative to light long-sleeved jerseys in transitional seasons. To ensure moisture is wicked away quickly and effectively, most designs are cut close to the body. To increase comfort and prevent chafing, manufacturers often use flat seams on the outside.